This invention relates to improvements in coordinate positioning apparatus and particularly to such an apparatus with an indexable and/or releasable stylus.
A coordinate positioning machine includes a support for a workpiece, a stylus or other sensing device (rangefinder, vision probe, etc.) for sensing points on a workpiece, and an assembly which supports the workpiece sensing device and permits it to move relative to the workpiece along coordinate axes which, in most cases, are a horizontal x-axis, a horizontal y-axis and a vertical z-axis. Position-indicating scales are provided to indicate the position of the machine head along the coordinate axes. (The term xe2x80x9cstylusxe2x80x9d is used in this specification without the intention of excluding other devices for sensing points on a workpiece.)
In early coordinate measuring machines, sometimes referred to as xe2x80x9chard probe machinesxe2x80x9d a stylus was rigidly connected to the head of the machine. A subsequent development was the touch-trigger probe which is mounted on the head and generates a digital signal when the stylus moves due to contact with the workpiece. Still another type of probe is an analog probe which provides signals indicating the magnitude of displacements which occur between the stylus and the head of the machine. A probe of the latter type which provides such signals along three mutually perpendicular axes is disclosed in U.S. Pat. No. 5,222,034 issued to the present inventor on Jun. 22, 1993, the entirety of which is incorporated into this specification by reference.
It is customary in the metrology field to provide coordinate measuring machines with a number of interchangeable styli which are selected and used depending upon the nature of the task at hand. In some situations, the styli are mounted on the head by threaded connections. Magnetically retained styli have also been utilized, wherein two releasable coupling members are held together magnetically.
Indexable probes are known in the art as exemplified by U.S. Pat. Nos. 4,313,263, 4,571,847, and 5,185,936. In each of these systems, a probe is supported by an indexing mechanism, and a stylus is supported by the probe. In U.S. Pat. Nos. 4,313,263 and 4,571,847, indexing is achieved by engaging the stylus with a stationary object and moving the probe so that an indexable (but not releasable) coupling moves from one indexed position to another. In U.S. Pat. No. 5,185,936, the positioning elements on the probe-supporting coupling are forced apart mechanically, and a motor turns a drive dog shaft to index the coupling.
The indexing mechanisms disclosed in U.S. Pat. Nos. 4,313,263, 4,571,847, and 5,185,936. In these products, the z-rail of a machine supports styli and their respective analog or touch trigger probes. Such probes have been held on machines by releasable couplings. Due to the high cost of probes this has been very costly for machines which require the ability to perform diverse tasks. Although it is possible to support analog or touch trigger probes using the apparatus from the coupling of the present invention, it is preferred, for reasons of cost reduction, to use the coupling to connect a stylus to a probe.
Prior indexing couplings have included electrical motors which provide the angular movement for reorientation. Such motors generate heat and thus are a source of errors as they raise the temperature in localized areas of the apparatus, causing distortions which adversely affect the accuracy of any resulting measurements.
The present invention adds significantly to the versatility of a coordinate positioning apparatus in a manner which is convenient, relatively inexpensive, and without impairing the accuracy of the machine.
The present invention provides a coordinate measuring machine in which a stylus is easily and conveniently reoriented and/or removed from the machine. A preferred embodiment of the invention is disclosed in the accompanying drawings and in the following description.
Some existing coordinate measuring machines are provided with indexable analog or touch trigger probes which detect movement of a stylus relative to the probe. In such arrangements, the probes themselves have been indexable, in contrast to preferred embodiments of the present invention in which a stylus is indexable relative to the probe. When interchangeable styli are used in the prior arrangements, interchangeable probes are also required, thus adding to the expense of the apparatus because probes are expensive and multiple probes are required.
In some coordinate measuring machines, storage docks have been provided for interchangeable probes, their styli, and couplings which support the probes. Due to the shapes of these couplings and their storage docks, the couplings require a specific angular orientation in order to fit into a storage dock. These couplings sometimes carry a cluster of styli, some of which encroach into the storage spaces of adjacent storage docks. Such encroachment can be minimized by one feature of the present invention, whereby interchangeable couplings will be accepted by their storage docks at any angle. This permits the preorientation of a coupling at any angle which will minimize potential encroachment by its styli into storage docks which are adjacent to it.
One object of the invention is to provide an effective method of operating a coordinate positioning machine by utilizing an indexing dock with a mechanism and motor which are not incorporated into the probe and stylus assembly, thus simplifying such assemblies and eliminating from them the indexing motor which can create errors due to heat emitted by an indexing motor.
Another object is to reduce the cost of providing a coordinate positioning machine with stylus indexing capabilities, this objective being realized by providing only one indexing dock which can serve multiple probe and stylus assemblies, and by providing indexable couplings between the probes and their styli rather than between the machine head and the probe.
Still another object of the invention is to provide a coordinate positioning machine with a stylus storage system which is effective to store a number of stylus-carrying coupling members at orientations whereby the encroachment of their styli into the storage spaces of adjacent storage docks is reduced or eliminated.
Another object of the invention is to provide for coordinate positioning apparatus in which styli are mounted in a manner which is effective, uncomplicated, indexable, accurate, and/or capable of releasing a stylus when desired.
Other significant objects will be realized by persons familiar with the art, upon reading and understanding this specification.
In one respect, the invention involves a method for operating a coordinate positioning machine in which a stylus or other workpiece sensing device is connected to a movable member of the machine by a coupling assembly which includes first and second coupling members. The first coupling member is supported by a movable member of the machine, the second coupling member is supported by the first coupling member, and the stylus is supported by the second coupling member. The first and second coupling members respectively have first and second sets of positioning elements which are mutually engagable in a plurality of angular orientations about a coupling axis to provide a plurality of angularly indexed positions at which the second coupling member has stable and repeatable positions relative to the first coupling member. An indexing dock is provided for rotating the second coupling member about the coupling axis. The method involves the steps of moving the movable member of the machine to carry the coupling assembly and stylus or other workpiece sensing device to the indexing dock. The second coupling member is engaged with a rotatable carrier on the indexing dock, preferably after the second coupling member has been entirely disconnected from the first coupling member, and the carrier is rotated to rotate the second coupling member about the coupling axis, thus changing the angular orientation of the second coupling member relative to the first coupling member. The movable member of the machine is then moved to carry the probe and coupling assembly away from the indexing dock for continuing use or to a storage dock.
Another aspect of the invention is the indexing apparatus used for performing the above-mentioned method described above. This involves a coupling assembly which has a first coupling member supported by the movable member of the machine, a second coupling member which is supported by the first coupling member, and a stylus or other workpiece sensing device which is supported by the second coupling member. The coupling assembly has a coupling axis about which the second coupling member is angularly orientable relative to the first coupling member. First and second sets of positioning elements are provided on the first and second coupling members respectively. These sets of positioning elements are mutually engagable in a plurality of angular orientations about the coupling axis to provide a plurality of angularly indexed positions at which the second coupling member has stable and repeatable positions relative to the first coupling member. An indexing dock is used to change the angular orientation of the second coupling member relative to the first coupling member. The indexing dock has a carrier for engaging the second coupling member. The carrier is rotatable about the coupling axis to change the angular orientation of the second coupling member relative to the first coupling member.
To release second coupling member and its stylus thereon at the indexing dock, the invention preferably uses a coupling assembly in which one of the first and second coupling members includes an electromagnet which is normally deactivated when the coupling members are coupled together. The other coupling member has a permanent magnet which provides a magnetic field which attracts the coupling members into mutual contact. The coupling member has positioning elements which provide accurate and repeatable relative positioning between them. The electromagnet, when activated, repels the coupling members apart in order to uncouple the coupling assembly, thus releasing the stylus from the coordinate positioning machine.
To enhance the versatility of the apparatus, styli are mounted on a stylus mount which preferably is an integral part of the second coupling member. The stylus mount has a plurality of stylus-receiving mounting holes, the axes of which extend in different directions from the stylus mount axis and have different inclinations relative to the stylus mount axis.
The machine is preferably operated in a way which permits storage of unused styli and their associated couplings in a plurality of adjacent storage docks, with the coupling members oriented so that their styli do not encroach into the storage spaces of adjacent storage docks. This objective is realized by a coordinate measuring machine in which a movable member is supported and guided for movement along a set of coordinate axes, a releasable coupling is supported by the movable member, and the releasable coupling is releasable from the movable member to permit its replacement by another releasable coupling. A stylus is mounted on the releasable coupling member. The machine has a plurality of mutually adjacent storage docks with storage areas for holding a plurality of releasable coupling members and styli mounted thereon. The machine has means for rotating the releasable coupling member to a selected angle, and the releasable coupling is shaped to fit into a storage dock regardless of the angle selected, so that an angle can be selected to reduce encroachment of styli into the storage areas of adjacent storage docks.
An indexable coupling is preferably integrated between the stylus and an analog or digital probe which is operable to detect movement of the stylus relative to the probe. This is preferable to existing systems in which a movement-detecting probe itself indexable. Thus, according to another aspect of the invention, a coordinate measuring machine has a stylus for contacting a workpiece, and a probe which supports the stylus and is operable to detect movement of the stylus relative to the probe. The machine supports the probe for movement in the coordinate axis system. The stylus is supported from the probe by a coupling assembly which includes first and second coupling members. The first coupling member is supported by the probe, the second coupling member is supported by the first coupling member, and the stylus is supported by the second coupling member. The second coupling member is angularly orientable relative to the first coupling member about a coupling axis of the coupling assembly. The first and second coupling members are provided with first and second sets of positioning elements which are mutually engagable in a plurality of angular orientations about the coupling axis to provide at least twelve angularly indexed positions at which the second coupling member has stable and repeatable positions relative to the first coupling member.
This summary has stated only the primary characteristics the main claims filed with this specification. Other important features of the invention are recited in the dependent claims.